1. Field of the invention
The present invention relates to a superconducting thin film and a method for manufacturing the same, and more specifically to a superconducting thin film having at least an isolated superconducting region formed of oxide an material, and a method for manufacturing the same.
2. Description of Related Art
Elemental devices which utilize superconductivity operate at a higher speed with a lower power consumption so that they will have far better performance compared with semiconductor devices. The oxide superconductor material which has been recently advanced in study makes it possible to prepare superconducting devices which operate at relatively high temperature. Though a Josephson device is one of the most famous superconducting devices, logic circuits may be more easily assembled by using so called superconducting-base transistors or so called super-FETs (field effect transistor) which are three-terminal superconducting devices than by using Josephson devices which are two-terminal superconducting devices. Therefore, the superconducting-base transistor and the super-FET are more practical.
These superconducting devices have superconducting parts as superconducting electrodes, superconducting channels etc. These superconducting pans are usually formed of superconducting thin films.
To apply superconducting devices to various electronic equipments, these superconducting devices need to be incorporated within an IC (integrated circuit). There are many element devices on a substrate of an IC and each element device region is isolated. A superconducting thin film which has an isolated superconducting region is necessary to isolate a superconducting device region which is incorporated within IC. In case of a superconducting device formed of an oxide superconductor material which has been recently advanced in study, an oxide superconductor thin film which has an isolated superconducting region is necessary.
In the prior art, in order to isolate a superconducting region of an oxide superconductor thin film, a photoresist layer is deposited on a necessary portion of an oxide superconducting film and the deposited oxide superconductor thin film is etched back, until the exposing portion of the oxide superconductor thin film is removed at all and a surface of beneath layer exposes.
There is another conventional method in order to prepare an oxide superconductor thin film which has an isolated superconducting region, in which an oxide superconductor thin film is deposited on a substrate which has a SiO.sub.2 layer where an isolation region will be formed. Si included in the SiO.sub.2 layer defuses into a portion of the oxide superconductor thin film on the SiO.sub.2 layer, so that the portion of the oxide superconductor thin film loses its superconductivity and changes into isolation region.
However, because of side etching etc., it is very difficult to conduct a fine processing by the etching process which uses a photoresist. In addition, a surface of an oxide superconductor thin film on which a photoresist layer is deposited will be contaminated by the photoresist. A side surface of an oxide superconductor thin film, which is exposed by etching is also contaminated by etchant. Since oxide superconducting material is easily degraded by water and Cl ion, it is difficult to prepare a superconducting device of good property with an oxide superconductor material by a process in which an oxide superconductor thin film is processed by etching.
An oxide superconductor thin film which is deposited on a substrate which has a SiO.sub.2 layer on a portion of its surface is not degraded. However, a step portion is produced on the surface of this oxide superconductor thin film at the edge of the SiO.sub.2 layer. In order to prepare a superconducting device, other material layers must be stacked on the oxide superconductor thin film. Because of the step portion of the surface of the oxide superconductor thin film, a stacked structure including the oxide superconductor thin film and other material layers on it is not of good quality. Therefore, it is difficult to form a multilayer structure including the oxide superconductor thin film and to form a fine structure. Further more, the problems of low withstand voltage of the step portion of the isolation region of the oxide superconductor thin film occur.